Improved accuracy for calibrated mass distribution measurements of bimetallic nanoparticles

Implementation of hybrid nanoparticles (HNPs), consisting of two different metal components, into applied systems has been hindered by an incomplete understanding of structural and chemical properties responsible for their enhanced, yet inconsistent performance. To address this persistent need, our work focused on using the electrospray differential mobility analyzer hyphenated to inductively coupled plasma mass spectrometry (ES-DMA-ICP-MS) to determine mass distributions across the entire NP distribution. Although previous work had applied similar hyphenated measurements to HNP systems, no efforts to develop accurate calibration methods for quantifying NP, and especially HNP, masses have been reported. We chose gold titania catalyst HNPs (Au@TiO2: 4 nm gold NPs adsorbed on 100 nm-300 nm TiO2 NPs) as a representative system because a large body of research exists on this topic. When we used ionic standards and compared it to our Au@TiO2 control, a reproducible difference in the slope was observed that led to an overestimation of both gold (Au) and titanium (Ti) by nearly a factor of four for the HNPs, demonstrating the complexity of quantification and the need to both develop a validated calibration method and identify the major sources for uncertainty in quantification. We determined the mass quantification discrepancy derived from the metal oxide NPs (independent of the presence of Au) and was caused by the DMA and ES (not the ICP-MS). Corrections were made for multiple charging that significantly improved the agreement between the ionic standard and Au@TiO2 metal quantification. Discussion on material properties for improved accuracy across different shapes, sizes, compositions, and surface chemistries is also included to demonstrate the general utility of the calibration across a broad number of fields. ES-DMA-ICP-MS is a powerful technique that provides statistically significant data for simultaneous determination of mass distributions of multi-element HNP systems across the entire sample population and should enhance characterization and development of HNPs when coupled with current core methods.

Automated summary

This study used ES-DMA-ICP-MS technique to analyze the mass distribution of hybrid nanoparticles and developed an effective calibration method. It identified the sources of uncertainty in mass quantification and made corrections to improve quantification accuracy. The calibration method demonstrated utility across different material properties.